Water-conducting roots responsible for nitrogen uptake in maize (Zea mays)

Nitrate (NO3-) uptake is primarily driven by mass flow and varies among maize root types. The importance of embryonic and crown roots in acquiring NO3- was determined here in wet and dry soils. Maize was grown in a split-root pot that segregated the embryonic and crown roots. The soil was moistened to water potentials of either -5kPa or -30kPa. A partial N mass balance was made by destructively sampling shoots, roots, and soils after 0, 24, and 48 h following 15N-KNO3 injection at the V3 and V6 stages. Gross nitrification was assessed using a 15N isotope dilution technique. At the V3 stage, crown roots had 202% more N uptake than embryonic roots in wet soil (-5 kPa). However, in dry soil (-30 kPa), N uptake was similar for embryonic and crown roots, possibly due to an 80% reduction of hydraulic conductance in crown roots. By the V6 stage, crown roots dominated N uptake, with embryonic roots supplying < 20% of N uptake. Soil gross nitrification rate was similar for root types. The present studies indicated that maize NO3- uptake depends primarily on the crown roots, due to their capacity to extract water and NO3- from soil, even under dry conditions. HighlightThis study reveals how different maize root types contribute to nitrate uptake under varying soil moisture conditions, suggesting that soil water management is important to ensure optimal nitrogen uptake.